The invention relates to a hydraulic camshaft adjuster for an internal combustion engine with a mechanical spring element, and in particular to a camshaft adjuster having a stator and a rotor, with two pressure chambers formed between the stator and the rotor which are separated by a vane of the rotor.
Hydraulic camshaft adjusters, especially in a rotary vane or vane-cell construction, typically have a stator and a rotor mounted with a degree of rotational freedom relative to the stator. Between the stator and the rotor there are at least two pressure chambers, which act in opposite directions and which are separated from each other by a radially oriented vane of the rotor.
It has been shown that the operation of a hydraulic camshaft adjuster is not problematic especially when the internal combustion engine provides sufficient hydraulic pressure, so that the pressure chambers are filled sufficiently with the hydraulic medium. However, it has also been shown that when the internal combustion engine starts up, under some circumstances sufficient pressure of the hydraulic medium cannot be provided. This has the result that when the internal combustion engine starts up in this way, the control times do not correspond to the default positions, or an unstable position of the camshaft adjuster is set, which produces “unstable” control times. Furthermore, it can generate undesired vibrations, which can lead to undesired noise in addition to increased component wear.
For preventing such problems, mechanical locking devices are known. From DE 196 23 818 A1, a locking device is known with a locking element constructed as a locking pin, whose front-end region has a conical construction and is held without backlash in a bore, which has a conical longitudinal section or an elliptical cross section, in a cover of the camshaft adjuster in a locked position. The locking pin is spring loaded and has two hydraulic control surfaces, of which the first, end control surface is in hydraulic connection with a pressure chamber of the camshaft adjuster and a second control surface formed by a shoulder of the locking pin is in hydraulic connection with another pressure chamber acting in the opposite direction in the camshaft adjuster.
From DE 101 27 168 A1, a locking device is known, in which a locking pin interacts with a step-shaped locking groove, wherein different levels of the step-shaped locking groove correspond to different locking positions, for example, a farthest advanced angle, an intermediate position, and a farthest retarded angle.
From DE 102 53 496, a locking device is known, in which a first locking pin assumes a locked position between an end position ADVANCED and a middle position, while a second locking pin can assume a locked position between an end position RETARDED and the middle position. When the pressure of the hydraulic medium falls to zero, the first locking pin can be brought into the locked position, while the second locking pin further remains in the unlocked position. When the internal combustion engine starts up, the inner rotor is moved by a dragging moment of the camshaft towards RETARDED until the first locking pin reaches the middle position. At this point, the second locking pin also reaches the locked position. After a successful engine start, the regulator increases the pressure of the lubricant in a first lubricant line, a first pressure chamber, and in the region of the first locking pin. Therefore, the first locking pin is unlocked, while the second locking pin is held in pressure contact with the second middle stop. For transitioning to regulated operation, the regulator increases the pressure in the second pressure chamber, whereby the second locking pin is also unlocked, so that the inner rotor can move freely. A corresponding locking device is also known from U.S. Pat. No. 6,450,137 B2.
From DE 199 18 910 A1, a locking device is known, which has two locking pins that can be activated in the radial control direction.
From the unpublished patent application of the applicant with the internal filing number of the applicant E 2004 255 and the title “Locking device for a Camshaft Adjuster of an Internal Combustion Engine,” it is known to lock the camshaft adjuster in a single position, especially the end position, with two locking pins, which have different amounts of peripheral backlash and which are acted upon by different pressure chambers of the camshaft adjuster.
Furthermore, from the unpublished patent application of the applicant with the internal filing number of the applicant E 2005 161 and the title “Camshaft Adjuster with a Locking Device,” it is known to provide a locking element both in an end position ADVANCED and also in the region of an end position RETARDED and to provide, in particular, a third locking element in a middle position.
From the unpublished patent application of the applicant with the internal filing number of the applicant A 2004 03 and the title “Locking Device for a Camshaft Adjuster,” a hydraulic actuation of a locking element is known, in which reliable measures for preventing undesired actuation of the locking element are taken.
The previously explained hydraulic camshaft adjusters and the locking devices are based on the requirement that, in an operating situation, in which locking is desired (in the following “locking situation”), care must be taken that the rotational angle of the rotor relative to the stator is located in a desired range or at a defined rotational angle. Here, the angle can involve, in particular, the rotational angle correlating to the locking position or a rotational angle between the end position ADVANCED and the locking position. Also possible are rotational angle ranges, for which it is guaranteed that the locking position is reached automatically when the internal combustion engine is turned off or when the internal combustion engine is restarted.
For guaranteeing that the rotor is located in a previously defined range for a locking situation, various measures are known:
According to E 2005 161, a spring element can be used, which applies a force on the rotor in the direction of the desired rotational angle range or the rotational angle coinciding with the locking position. Such a spring element, however, requires additional installation space.
From the unpublished patent application of the applicant with the internal filing number of the applicant E 2004 332 and the title “Method for Operating a Hydraulic Camshaft Adjuster,” it is known to use a shutdown predictor, which indicates that locking of the camshaft adjuster is likely or required, for example, because the internal combustion engine is set for operation in the future. For the case that the shutdown predictor indicates that the locking is required, a force is applied to the camshaft adjuster automatically via a control unit, such that
a) the camshaft adjuster moves in the direction of the locking position or
b) it moves into a rotational angle lying between the locking position and an end position ADVANCED.
On the other hand, it has been shown that influencing the force relationships in a camshaft adjuster via a spring element can also be desirable independent of any end position locking:
U.S. Pat. No. 6,311,654 B1 addresses the problem that a hydraulic pump for charging the pressure chambers is typically driven by a crankshaft, which has the result that the flow of hydraulic means is reduced, under some circumstances, at a low rotational speed of the internal combustion engine. This can lead to an undesired adjustment of the camshaft adjuster.
For overcoming problems of the previously explained type, JP A 9 264 110 proposes to connect a torsion spring between a driving element and a driven element. For this purpose, the torsion spring is supported in the housing of the camshaft adjuster with one foot on the chain wheel, while the other foot of the torsion spring is supported on the rotor.
This solution is considered problematic according to U.S. Pat. No. 6,311,654 B1 because, under some circumstances, a bypass between the pressure chambers of the camshaft adjuster can be created via the receptacle for the torsion spring, which can lead to undesired operating states up to breakdown of the camshaft adjuster. For preventing such problems, U.S. Pat. No. 6,311,654 B1 proposes to arrange the pressure chambers and the vanes radially outside of the receptacle for the torsion spring element, so that in a radial intermediate space in the housing, a suitable seal can be realized. In this way, however, the total radial installation size of the camshaft adjuster is increased. Such enlarged radial dimensions can be prevented according to U.S. Pat. No. 6,311,654 B1 in that the pressure chambers on one hand and the receptacle for the torsion springs on the other hand are arranged axially one next to the other with radially overlapping extensions. Transferring the hydraulic medium between individual pressure chambers via the receptacle for the spring element is prevented by a circular ring-shaped separating disk, which is connected axially between the pressure chambers and the receptacle.
From DE 40 32 586 A1, a camshaft adjuster is known, which is actuated by a control piston and in which a torsion spring arrangement is arranged parallel to the adjustment chambers between a driving wheel and a camshaft. This torsion spring arrangement is used for transmitting an approximately average torque. This construction is based on the knowledge that for adjustments in different directions, torques must be generated in the camshaft adjuster, which have opposing directions, whose magnitudes, however, are different for different directions, under some circumstances, so that, for example, through the movement of the drive and/or the frictional relationships, an average moment for the torque requirements for different adjustment directions can be produced, which is not equal to zero. To limit the moment to be generated in the camshaft adjuster to the difference of the required extremes from the average moment—and not to the, under some circumstances, greater absolute extreme—the publication proposes to supply the average moment via an energy accumulator, which is constructed as a torsion-spring arrangement connected parallel to the adjustment chambers between the driving wheel and the camshaft. The torsion-spring arrangement is constructed separately from the camshaft adjuster.
DE 690 28 063 T2 discloses another construction of using torsion-spring elements for influencing the moment relationships for a camshaft adjuster.